I have been pretty happy with this case so far. It is pretty much the perfect setup for a dedicated hashcat system. It supports 6 GPUs on risers with plenty spacing for good airflow. It is actually really quiet under load since it runs so much cooler than my old setup.

Don't the fans on the back only block the blown-out air of the cards? And are there no front fans to provide airflow through the whole case? From what it looks like it would be more useful to have the fans placed before the cards (in the middle of the case). Especially with 6 cards the cards will take care of blowing warm air out of the case.

Maybe you are looking at it backwards? There are no fans on the back. The fans are on the front (intake) to pull cool are into the chassis across the cards and out the back of the case. There is also a mounting plate in the middle of the case to add three more fans but I am not using it because it isn't needed for only 3 cards. The rear plate also has room for two power supplies.

Ah, I understand what you are saying now. I think you are talking about GPUs with reference style coolers that use a squirrel cage fan (blower) to push air out the back plate of the card. In that case it might be better to reverse the airflow in the chassis so the exhaust is coming out of the front. Since the cards I have are not using the reference coolers (they just use regular fans) it doesn't really matter what direction the airflow is moving in the chassis.

With 6 GPUs installed you will need better fans than I am using. The fans I am using don't have much static pressure but they are quieter and still good enough for 3 GPUs. Keeping 6 GPUs cool should still be pretty easy to manage with some higher CFM fans since there is plenty of airspace between the cards to keep the air flowing through the chassis. I am waiting to see how the Maxwell GPUs perform before I decide to add any more GPUs to my system.

The guy that designed these cases posted this comment and screenshot from one of his scrypt mining systems with 5 MSI R9 280X GPUs.
"Current setup has 3x 140cfm fans front and 3x 100cfm fans mid. AC is set to cycle about every 30 min. Temps never go above 80c."

If you take a closer look at the back view it has two PSU mounts. One is on the side of the systemboard the other is above the pci-e slots on the systemboard (where I mounted my hard drive). Since this case uses PCI-E risers for the GPUS the second power supply wont get in the way.